The major objectives of this research are to determine the effects of providing patients a degree of control and/or predictability in health care settings where, typically, little control and/or predictability exist and to investigate whether the effects are mediated by the patients' desire for control in those settings. The social-psychological literature has presented evidence of the negative consequences of loss of control and of the potential benefits of increasing individuals' control; many of these studies, however, have been carried out only in laboratories. Few field experiments have been conducted in actual health care settings. Also individual differences among patients have been almost totally ignored. Two known-groups validation studies and three field experiments are proposed. The validation studies will assess the usefulness of two new individual difference measures: the Expectation of Control (EC) and Desire for Control (DC) Scales; it is then planned to use these measures in three proposed field settings where patients' degree of control and/or predictability will be manipulated. Control will be operationalized by giving patients choices over selected aspects of their care; predictability will be operationalized by giving patients information about the care they will receive. The experiments will be conducted in different health care settings, each operationalizing control (i.e., choice) in a slightly different way. Previous research has implied that the absence of control and/or predictability is stressful and that providing control and/or predictability is stress reducing. In this research, patients' stress reactions will be measured using a multivariate approach. All experiments will include behavioral, subjective, and physiological indices as dependent variables. The research will investigate whether giving information is as stress reducing as allowing patients choices; we also hope to demonstrate that the presence or absence of control most affects those who desire control.